NUCLEAR MATRIX ASSOCIATED OPIOID BINDING-SITES ARE INCREASED UPON D-ALA(2)-D-LEU(5)-ENKEPHALIN-INDUCED DOWN-REGULATION IN NG108-15 CELLS

Nuclear matrix preparations obtained from purified nuclei of NG108-15 cells, display high affinity opioid antagonist binding (1). Under cond itions of opioid agonist-induced desensitization of cell surface recep tors, nuclear matrix associated opioid to (membranes binding was aboli shed, but expectedly binding densities in P-20 (membranes sedimenting at 20,000 g) were unaffected. Here, binding changes were monitored in P-20 and nuclear matrix fractions during agonist-induced down-regulati on. D-Ala(2)-D-Leu(5)-enkephalin (DADLE, 0.1 mu M, 1 h) treatment of N G108-15 cells caused an increase in nuclear matrix-associated binding, while diminishing that in P-20. Taken together with other findings, t hese results suggest that a subpopulation of opioid binding sites, ori ginally in the plasma membrane, are internalized and migrate to the nu clear matrix.